OK, we've heard that enzymes are an important class of proteins and that they help reactions occur. Show me!
We will do two experiments to see enzymes at work.
First take a piece of white bread and chew it. Keep chewing! Do not swallow!!
After a while, you should notice that the bread starts to taste a little sweet. This is because an enzyme in your saliva is breaking down the starch in the bread to release sugar.
When you've had enough, you'll probably want to spit the bread out!
Enough of that! Show me something else...
Let's try another experiment. Have you ever had a pineapple jelly? Almost certainly not - and there is a very good reason why!
Cut the bottom (not the leafy end) off your pineapple - about 1-2cm should be enough. Now cut another slice about 1-2cm thick and place that slice on top of a jelly that you have already prepared.
Now you need to leave your jelly and pineapple somewhere it won't get disturbed. Don't put it in the fridge, but leave it at room temperature. You need to leave it for at least an hour, a couple of hours would be better.
Carry on with the rest of this session and come back to your pineapple jelly at the end.
What you should find is that the pineaple has started to sink into the jelly. This is because the pineapple contains an enzyme which breaks down the gellatin in the jelly. If you leave it long enough, it will eat its way right down through the jelly!
That's why you don't get pineapple jellies - if you made a jelly containing chunks of pineapple, the pineapple would eat away at the jelly around it.
You might want to do some further experiments. Do other fruits work in the same way? How could you do a 'control' experiment to see that it is not just the pressure of the weight of the pineapple slice which makes the jelly dissolve?